1. Field of the Invention
This invention relates to a process for producing a 3-iminohaloisoindoline-1-one useful as an intermediate for preparing quality organic pigments having high purity, excellent fastness to light and good resistance to heat.
2. Description of the Prior Art
Many methods are known for producing a 3-iminohaloisoindoline-1-one by using a specific reactant and a specific starting material such as a halophthalimide, a halophthalic anhydride and a halo-phthalodinitrile. Such processes are described, for example, in Japanese Patent Publication Nos. 4488/59, 1643/61, 3826/61 and 4521/61 and U.S. Pat. No. 3,887,581.
Of these methods, the process of U.S. Pat. No. 3,887,581 is particularly attractive industrially because the process is conducted using mild reaction conditions and a readily available starting material. Further, the process of this patent is simpler than the other processes. More specifically, according to the process of U.S. Pat. 3,887,581 a halophthalodinitrile is hydrated in the presence of an alkali metal hydroxide, an alkaline earth metal hydroxide, or a compound forming such hydroxides at a temperature of 10.degree. to 100.degree. C. for a time of from 0.5 to 40 hours.
The product thus obtained is mainly an alkali metal salt or alkaline earth metal salt of the 3-iminohalogenoisoindoline-1-one. Accordingly, it is necessary to further hydrolyze the salt with an acid to obtain the 3-iminohaloisoindoline-1-one. Furthermore, the purity of the 3-iminohaloisoindoline-1-one and its salt obtained by such a process is disadvantageously insufficient for use as a starting material for preparing quality organic pigments, and the pigments prepared therefrom contain inseparable impurities, with the result that the pigments are inferior in the clearness and vividness of color. Clearness and vividness are, of course, important characteristics of coloring agents.
Extensive investigations have been made in order to avoid the above-described disadvantages, and to directly obtain a 3-iminohaloisoindoline-1-one having high purity in high yields from a halophthalodinitrile.